Silicon is employed in a wide variety of applications. In the electronics industry, high-purity silicon crystals having specifically modified electronic properties are used. The high costs associated with production of these crystals only contribute slightly to the overall costs of an individual component due to the low area requirement of the individual electronic components produced therefrom. For use of silicon in photovoltaic technology, high-purity silicon is again employed for the production of high-power and concentrator cells. In this case, the purity does not relate only to metallic foreign atoms, alkaline earth metal elements, boron and phosphorus, but also to carbon and oxygen. In spite of extensive literature few details are known on the action of oxygen and carbon on the electrical properties of solar cells. These two elements are thus known as pronounced troublemakers (see: D. Helmreich, H. Seiter, D. Huber and R. Wahlich, Defect Interaction in "Solar" Silicon, IEEE 1982, pages 405 ff).
In polycrystalline silicon for terrestrial solar cells which is intended to meet the economic demands on large-scale photovoltaic technology, somewhat higher oxygen and carbon contents than in high-purity monocrystals for the electronics industry have to be accepted. However, these materials which can be produced economically have the disadvantage of only relatively low efficiency.
The object of the invention is thus to provide silicon which is suitable for photovoltaic technology and with which improved efficiency can be achieved and which can be obtained economically.